Magnetic systems with irreversible characteristics and a method of manufacturing and repairing and operating such systems

ABSTRACT

A novel magnetic data storage system and a sensing system of magnetic characteristics are disclosed; the systems have a magnetization direction that is irreversible in an external magnetic field. A method of manufacturing, a method of resetting or changing or repairing and a method of operating such systems are also disclosed. The systems can include a set of magnetic devices in a balancing configuration; essentially each of said devices comprises a structure of layers including at least a first ferromagnetic layer and a second ferromagnetic layer with at least a separation layer of a non-magnetic material there between, said structure having at least a magneto resistance effect. The magnetization direction of the first ferromagnetic layer of at least one of said devices is irreversible in an external magnetic field higher than about 35 kA/m.

FIELD OF THE INVENTION

The present invention is related to the field of magnetic devices. Morein particular, a magnetic data storage system and a sensing system ofmagnetic characteristics, the systems having a magnetization directionthat is irreversible in an external magnetic field, are disclosed. Amethod of manufacturing, a method of resetting or changing or repairingand a method of operating such systems are also disclosed.

BACKGROUND OF THE INVENTION

Magnetic devices are known in the art. Spin-valve structures such asGiant Magneto Resistance (GMR) and Spin-tunnel Magneto Resistance (TMR)devices recently have been extensively studied and were subject of avast number of disclosures. GMR- and TMR-devices comprise as a basicbuilding stack two ferromagnetic layers separated by a separation layerof a non-magnetic material. This structure in the sequel is referred toas the basic GMR- or TMR-stack of the magnetic device, or is referred toas the GMR- or TMR-structure. Such structure has magneto resistancecharacteristics and shows the GMR- or TMR-effect. The separation layeris a non-ferromagnetic metallic layer for GMR-devices, and is anon-metallic, preferably insulating, layer for TMR-devices. Over theseparation layer, there is a magnetic coupling between the twoferromagnetic layers. The insulating layer in the TMR-devices allows fora significant probability for quantum mechanical tunneling of electronsbetween the two ferromagnetic layers. Of the two ferromagnetic layers,one is a so-called free layer, and one is a so-called pinned or hardlayer. The free layer is a layer whose magnetization direction can bechanged by applied magnetic fields with a strength lower, preferablysubstantially lower, than the strength of the field required forchanging the magnetization direction of the pinned layer. Thus thepinned layer has a preferred, rather fixed magnetization direction,whereas the magnetization direction of the free layer can be changedquite easily under an external applied field.

The hard layer can consist of a hard magnetic material or of arelatively soft magnetic material pinned by exchanged biasing to anAnti-Ferromagnetic (AF) layer, or it can consist of anArtificial-Anti-Ferromagnet (AAF) consisting of two or more magneticlayers coupled in an anti-parallel direction by an appropriateintermediate non-magnetic coupling layer. The AAF can be biased by an AFlayer to make it even more rigid and to define a single-valuedmagnetization direction of the AAF.

A change of the magnetization of the free layer changes the resistanceof the TMR- or GMR-device. This results in the so-called magnetoresistance effect or GMR/TMR effect of these devices. The electricalresistance of the TMR- or GMR-device changes in a predictable manner inresponse to a varying magnetic field, making the devices suitable foruse as magnetic-electrical transducers in a sensing system of a magneticfield. The characteristics of these magnetic devices or systems can beexploited in different ways. For example a spin valve read-out elementutilizing the GMR-effect can be used for advanced hard disk thin filmread heads. Also stand-alone magnetic memory systems (MRAMs) ornon-volatile embedded memory systems can be made based on the GMR- orTMR-devices.

A further application is a sensor device or system for magneticcharacteristics. Such sensing systems are used for example in anti-lockbraking (ABS) systems or other automotive applications.

It is often required in a number of applications to clearly distinguishbetween the response of the sensor system (resistance changes) due to(varying) magnetic field and the response of the sensing system(resistance changes) due to environmental factors such as temperaturevariations. One approach in solving this problem consists in connectinga number of GMR- or TMR-devices in a Wheatstone bridge arrangement. If apair of GMR or TMR devices can be magnetically biased in such a manneras to have opposite responses (in the sense of opposite polarity) to agiven magnetic field but not to other environmental factors, thensubtractive comparison of the electrical resistances of the two GMR orTMR devices will cause cancellation of any unwanted response to spuriousenvironmental factors, while exposing any response to magnetic field.

Magnetic field sensing system employing a Wheatstone bridge in thismanner are known from the prior art. However, among the sensing systemthus known, there are various different approaches when it comes tomagnetically biasing the magneto-resistive devices.

For example: in Japanese patent application (Kokai) No. 61-711 (A), eachof the resistive devices in the Wheatstone bridge is magnetically biasedin a given direction using an appropriately poled permanent magnetpositioned in the vicinity of that device; on the other hand, in anarticle in Philips Electronic Components and Materials TechnicalPublication 268 (1988) entitled “The magnetoresistive sensor” theindividual resistive devices are biased using a so-called “barber pole”(a term generally known and understood in the art, and thus receiving nofurther elucidation here).

The use of biasing on the basis of permanent magnets as in case (a)above is highly unsatisfactory: not only is very careful tuning of thestrength and position of the permanent magnets required, but thepermanent magnets are themselves unacceptably sensitive to temperaturevariations. In addition, the use of permanent magnets necessarily makesany such biased magnetic field sensor bulky, and sets a limit on theattainable degree of miniaturization. On the other hand, while thebiasing method in case (b) may be suitable for resistive devicesdemonstrating the so-called Anisotropic Magneto-Resistive (AMR) effect,it cannot be employed in conjunction with resistive devicesdemonstrating the GMR or TMR effect.

In the prior art document J. Daughton, J. Brown, E. Chen, R. Beech, A.Pohm and W. Kude, “Magnetic field sensors using GMR multilayer”, IEEETrans. Magn. 30, 4608 (1994), two (of the four) bridge elements aremagnetically shielded, the shields may be used as flux concentrators forthe two sensitive device.

Freitas in “Giant magnetoresistive sensors for rotational speedcontrol”, J. Appl. Phys. 85, 5459 (1999) suggests that two (of the four)bridge devices are “inactivated” by depositing them on a roughened partof the substrate.

Another approach devolves on integrating an isolated conductor below orover the sensor elements (consisting of exchange-biased spin valves) toinduce a magnetic field that “sets” the exchange-biasing direction ofthe device in opposite directions, while the devices are heated abovethe blocking temperature of the exchange-biasing material R. Coehoornand G. F. A van de Walle, “A magnetic field sensor, an instrumentcomprising such a sensor and a method of manufacturing such a sensor”,patent application EP 95913296.0, now granted, and J. K. Spong, V. S.Speriosu, R. E. Fontana Jr., M. M. Dovek and T. L. Hylton, “Giant andmagnetoresistive spin valve bridge sensor”, IEEE Trans. Magn.32, 366(1996); M. M. Dovek, R. E. Fontana Jr., V. S. Speriosu and J. K. Spong,“Bridge circuit magnetic field sensor having spin valve magnetoresistiveelements formed on common substrate”, U.S. Pat. No. 5,561,368. Acomparable method with an integrated conductor has been proposed forelements based on an Artificial Antiferromagnet (AAF) by W. Schelter andH. van den Berg in “Magnetfeldsensor mit einer Brückenschaltung vonmagnetoresistiven Brückenelementen”, DE 19520206 (01.06.95).

In the patent application WO 9638738-A1 “Magnetoresistive thin-filmelements-uses adjustment current at high temp. to regulate magnetizationdistribution of bias layer of sensor elements arranged in bridgecircuit, and includes cooling body” (Ger) it is suggested that in thefactory the magnetizations are set in opposite directions in differentbranches of the bridges by exposing a wafer with sensor structures to anexternal magnetic field that is induced by a kind of “stamp” comprisinga pattern of current carrying conductors which is brought in thevicinity of the wafer.

These prior art solutions are rather complicated and require quite someeffort in practice. Moreover, the possibilities disclosed in J.Daughton, J. Brown, E. Chen, R. Beech, A. Pohln and W. Kude, “Magneticfield sensors using GMR multilayer”, IEEE Trans. Magn. 30, 4608 (1994),and Freitas “Giant magnetoresistive sensors for rotational speedcontrol”, J. Appl. Phys. 85, 5459 (1999) only allow the realization of ahalf-bridge and therefore loose half of the possible output signal orresponse. The magnetic fields that can be realized with the optionssuggested by R. Coehoorn and G. F. A van de Walle, “A magnetic fieldsensor, an instrument comprising such a sensor and a method ofmanufacturing such a sensor” and J. K. Spong, V. S. Speriosu, R. E.Fontana Jr., M. M. Dovek and T. L. Hylton, “Giant and magnetoresistivespin valve bridge sensor”, IEEE Trans. Magn.32, 366 (1996); M. M. Dovek,R. E. Fontana Jr., V. S. Speriosu and J. K. Spong, “Bridge circuitmagnetic field sensor having spin valve magnetoresistive elements formedon common substrate”, U.S. Pat. No. 5,561,368 (04.11.94) and W. Schelterand H. van den Berg in “Magnetfeldsensor mit einer Brückenschaltung vonmagnetoresistiven Brückenelementen”, DE 19520206 are very limited instrength, because the currents have to be relatively small in the(necessarily narrow and thin) conductors. Further, the options disclosedin J. Daughton, J. Brown, E. Chen, R. Beech, A. Pohm and W. Kude,“Magnetic field sensors using GMR multilayer”, IEEE Trans. Magn. 30,4608 (1994), R. Coehoorn and G. F. A van de Walle, “A magnetic fieldsensor, an instrument comprising such a sensor and a method ofmanufacturing such a sensor” and J. K. Spong, V. S. Speriosu, R. E.Fontana Jr., M. M. Dovek and T. L. Hylton, “Giant and magnetoresistivespin valve bridge sensor”, IEEE Trans. Magn.32, 366 (1996); M. M. Dovek,R. E. Fontana Jr., V. S. Speriosu and J. K. Spong, “Bridge circuitmagnetic field sensor having spin valve magnetoresistive elements formedon common substrate”, U.S. Pat. No. 5,561,368 (04.11.94) require severalextra processing steps (both for patterning and isolation of theconductors or shields), which makes the sensors more expensive andreduces the fabrication yield. If the method suggested in the patentapplication WO 9638738-A1 “Magnetization device for magnetoresistivethin-film elements-uses adjustment current at high temp. to regulatemagnetization distribution of bias layer of sensor elements arranged inbridge circuit, and includes cooling body is used, the sensor can bedestroyed if exposed to magnetic field of the same strength (or larger)as the field used during setting the magnetization directions.

In particular for automotive applications, but also for read heads, therobustness of the sensing system becomes more and more important. Thistrend makes setting of magnetization directions after deposition of theelements more and more difficult. In sensing systems that have tooperate in relatively large magnetic fields, as required in for instanceautomotive applications, the hard magnetic layer should be as hard aspossible. This makes a definition of the hard magnetization directionafter deposition less attractive since it puts an upper limit to the“hardness” of the magnetic reference layer, otherwise the magnetizationdirection of this hard layer cannot be set. For example, the sensingsystems as disclosed in WO 96/38740 and WO 96/38738 can not be used inmagnetic fields stronger than 15 kA/m (18 mT) since this may change thedirection of the hard magnetic reference direction. For automotiveapplications, typically magnetic bias fields of 5-100 mT are used.

In Wheatstone bridge configurations, it is needed that the four devicesthat make the Wheatstone bridge are identical and therefore preferablyare made under a uniform manufacturing condition. This uniformmanufacturing condition may be a uniform deposition condition for alldevices of the sensing system but at the end of the manufacturing cycletwo devices with opposite exchange biasing directions are needed.

SUMMARY OF THE INVENTION

It is an aim of the present invention to disclose a sensing system for amagnetic characteristic and a magnetic data storage system that arerobust and that have at least one magnetic characteristic that isirreversible in an external magnetic field. It is another aim of thepresent invention to disclose a sensing system for a magneticcharacteristic that can combine different magnetization directionswithin a limited space such as a single substrate or a single chip andtherefore allows for a further miniaturization of the sensing systems.Also a data storage system is disclosed that can combine differentmagnetization directions within a limited space such as a singlesubstrate or a single chip and therefore allows for a furtherminiaturization of the sensing systems. It is a further aim of thepresent invention to disclose a method of manufacturing a sensing systemand/or a magnetic data storage system of which the magnetizationdirection of at least part of at least one of the devices can be setduring manufacturing of the system, and for which the processing issimple and requires only a limited number or no extra processing steps.It is yet another aim of the present invention to disclose a method ofmanufacturing a sensing system of magnetic characteristics and/ormagnetic data storage system that can combine different magnetizationdirections within a limited space such as a single substrate or a singlechip and therefore does not pose strict limits on miniaturization of thesystem.

Several aspects of the invention are summarized herebelow. The differentaspects and embodiments of the invention that are explained in thissection and throughout the whole specification can be combined as and tothe extent the person of skill in the art is able to appreciate. Anumber of terms that is used in this summary and throughout thespecification is explained at the end of this section.

In a first aspect of the present invention a sensing system of amagnetic characteristic is disclosed. Said system includes a set ofmagnetic devices in a balancing configuration and essentially each ofsaid devices comprises a structure of layers including at least a firstferromagnetic layer and a second ferromagnetic layer with at least aseparation layer of a non-magnetic material therebetween, said structurehaving at least a magneto resistance effect, and wherein themagnetization direction of the first ferromagnetic layer of at least oneof said devices is irreversible in an external magnetic field with avalue higher than about 35 kA/m . The value of the external magneticfield can also be higher than about 40 or 50 or 60 kA/m. The externalmagnetic field can also have value in a range of about 35 kA/m to about2 MA/m or even 200 MA/m. Preferably the first ferromagnetic layer is thepinned or hard ferromagnetic layer.

The ferromagnetic layers of the devices of the sensing system of theinvention may be composed of several layers and other intermediatelayers may be present in the stack of layers. In an embodiment of theinvention, at least one of the devices of the sensing system includes anArtificial AntiFerromagnet (AAF) structure. An AAF is a magneticmultilayer structure that includes alternating ferromagnetic andnon-magnetic layers which have an exchange coupling that results in anantiparallel orientation of the ferromagnetic layers in the absence ofan external magnetic field. Such result can be achieved throughappropriately choosing the materials and layer thicknesses of the AAFmultilayer stack. Each of the ferromagnetic layers of the AAF canconsist of subsystems of other ferromagnetic materials. The sensingsystem can also include an exchange-biased AAF magnetic multilayerstructure. The exchange-biased AAF can include an exchange biasing layerof IrMn, FeMn, NiMn, PtMn or NiO type material, said exchange biasinglayer being adjacent to, and in contact with, the AAF-structure.

In another embodiment of this first aspect of the invention, the sensingsystem can comprise at least four (or even at least two) magneticdevices being positioned in a two by two grouped, preferably at leastpair-like, configuration with a contact area between the groups (pairs)and with the magnetization direction of the first ferromagnetic layerbeing substantially opposite for the devices of different groups (pairs)and being substantially identical for the devices of the same group(pair). Preferably the first ferromagnetic layer is the pinned or hardferromagnetic layer.

In yet another embodiment of this first aspect of the invention, thesensing system can have at least four (or even at least two) magneticdevices being positioned in a grouped, preferably at least two by twopair-like configuration, with a first group (pair) of devices withsubstantially the same magnetization direction of the firstferromagnetic layer of the devices under an angle of about 90 degreeswith a second group (pair) of devices, the second group (pair) ofdevices having the first ferromagnetic layer with substantially the samemagnetization direction but under an angle of about 90 degrees withrespect to the magnetization direction of the first ferromagnetic layerof the first group (pair) of devices, and with a contact area.Preferably the first ferromagnetic layer is the pinned or hardferromagnetic layer.

In a second aspect of the present invention, a method of manufacturing asensing system of a magnetic characteristic is disclosed. The systemincludes a set of magnetic devices in a balancing configuration andessentially each of said devices comprises a structure of layersincluding at least a first ferromagnetic layer and a secondferromagnetic layer with at least a separation layer of a non-magneticmaterial therebetween, said structure having at least a magnetoresistance effect. The method comprises the step of heating part of thesystem including at least one of the devices of said set while applyingan external magnetic field over at least part of said system, the partincluding said at least one device. The part of the system that isheated can partly or completely coincide with the part of the systemthat is exposed to said external magnetic field. Thus localized heatingof the system in an external magnetic field is achieved. Preferably theexternal magnetic field is homogeneous over said part. The heating canbe achieved by applying a current pulse on or through the device. Theheating can also be achieved by applying a laser pulse or a pulse froman electron beam or ion beam on or through the device. Preferably atleast one of the devices is heated to a temperature in the range ofabout 50 to about 800° C., preferably in the range of about 300 or 400or about 600° C., while said external magnetic field has a value in therange of about 35 kA/m or 40 kA/m or 50 kA/m to 200 MA/m.

Localized heating of only one of the devices of the system in anexternal magnetic field can be achieved or all of the devices of saidset can be heated to the same temperature or at least two of the devicesof the set can be heated to a different temperature value. The externalmagnetic field directions can also be alternating over at least part ofsaid system. By applying this method of the invention, sensing systemswith multiple biasing directions of the devices in the system can beachieved. The devices have a thermally and magnetically robust materialstructure that is suited in for example automotive applications.

The method can be such that after the execution of the steps, the firstferromagnetic layer of said at least one device has a magnetizationdirection that is correlated to the direction of said external magneticfield, and preferably being irreversible in an external magnetic fieldhigher than about 35 kA/m.

In a third aspect of the present invention, a method of manufacturing asensing system of a magnetic characteristic is disclosed. The systemincludes a set of magnetic devices in a balancing configuration andessentially each of the devices comprises a structure of layersincluding at least a first ferromagnetic layer and a secondferromagnetic layer with at least a separation layer of a non-magneticmaterial therebetween, said structure having at least a magnetoresistance effect. The method comprises the steps of depositing saidstructure of layers of at least one of said devices on a substrate whileapplying at least during a time part of the deposition step an externalmagnetic field over at least part of said substrate. Preferably, theexternal magnetic field has at least one characteristic that is positiondependent over said substrate. Such characteristic can include themagnitude and/or the magnetization direction of said magnetic field.

During deposition, the substrate can be held in a deposition holder,said holder containing magnetic elements for applying said externalmagnetic field. After the execution of the method, the firstferromagnetic layer of said at least one device has a magnetizationdirection that is correlated to the direction of said external magneticfield and the magnetization direction of this first ferromagnetic layeris irreversible in an external magnetic field higher than about 35 kA/m.While executing the method according to the second aspect of theinvention, the substrate may also be heated.

In a fourth aspect of the present invention, a method of manufacturing asensing system of a magnetic characteristic is disclosed. The systemincludes a set of magnetic devices in a balancing configuration andessentially each of said devices comprising a structure of layersincluding at least a first ferromagnetic layer and a secondferromagnetic layer with at least a separation layer of a non-magneticmaterial therebetween, said first structure having at least a magnetoresistance effect. The method comprises the steps of depositing a firstferromagnetic layer of at least a first of the devices of said set whileapplying a magnetic field to pin the magnetization direction in thefirst ferromagnetic layer in a first direction (the first depositionstep) ; and thereafter depositing a first ferromagnetic layer of anotherof the devices of said set while applying a magnetic field to pin themagnetization direction in this first ferromagnetic layer in a seconddirection different from, preferably opposite to, the magnetizationdirection in the first ferromagnetic layer of the first device (thesecond deposition step). While executing the method according to thefourth aspect of the present invention, magnetic fields of opposingdirection can be applied during the first and the second depositionstep. The set of magnetic devices in a balancing configuration caninclude two full Wheatstone bridge arrangements, the magnetizationdirections in corresponding devices of the Wheatstone bridges beingpinned at different angles.

In a fifth aspect of the present invention, a deposition holder for asubstrate for depositing a structure of layers on said substrate isdisclosed, said holder containing magnetic elements for applying anexternal magnetic field over at least part of said substrate, saidexternal magnetic field having at least one magnetic characteristic thatis position dependent over said substrate. Said characteristic caninclude the magnitude and/or the magnetization direction of saidmagnetic field. The deposition holder can further comprise at least oneheating element for heating at least part of said substrate whileapplying said external magnetic field over said substrate. Thedeposition holder can also comprise magnetic elements for applying saidexternal magnetic field.

In a sixth aspect of the present invention, a method of manufacturing asensing system of a magnetic characteristic is disclosed. The systemincludes a set of magnetic devices in a balancing configuration andessentially each of said devices comprises a structure of layersincluding at least a first ferromagnetic layer and a secondferromagnetic layer with at least a separation layer of a non-magneticmaterial therebetween, said structure having at least a magnetoresistance effect. The method comprises the step of depositing a firstferromagnetic layer of said set of devices, said first ferromagneticlayer being part of an AAF-structure, thereafter orienting said firstferromagnetic layer of said set of devices, and thereafter depositingthe other layers of the AAF-structure and said second ferromagneticlayer and said separation layer of a non-magnetic material. The step oforienting the first ferromagnetic layer for example can be done byheating the set of devices in a spatially varying magnetic field.

In a seventh aspect of the present invention, a method of operating amagnetic system is disclosed, said system including a set of magneticdevices in a balancing configuration and essentially each of saiddevices comprising a structure of layers including at least a firstferromagnetic layer and a second ferromagnetic layer with at least aseparation layer of a non-magnetic material therebetween, said firststructure having at least a magneto resistance effect, the methodcomprising the step of alternating at least one of the magneticcharacteristics of at least one of the devices of said set by heatingsaid at least one device of said set while applying an external magneticfield over at least part of said system, the part including said atleast one device.

Preferably the system is a sensing system of a magnetic characteristicand includes a set of magnetic devices in a balancing configuration. Thesystem may also be a read head or a data storage system such as a MRAMmemory.

In an eighth aspect of the present invention, a method of resetting orrepairing or changing a magnetic system is disclosed, said systemincluding a set of magnetic devices and essentially each of said devicescomprising a structure of layers including at least a firstferromagnetic layer and a second ferromagnetic layer with at least aseparation layer of a non-magnetic material therebetween, said firststructure having at least a magneto resistance effect, the methodcomprising the step of alternating at least one of the magneticcharacteristics of at least one of the devices of said set by heatingsaid at least one device of said set while applying an external magneticfield over at least part of said system, the part including said atleast one device. Preferably the system is a sensing system of amagnetic characteristic and includes a set of magnetic devices in abalancing configuration. The system may also be a read head or a datastorage system such as a MRAM memory.

In a ninth aspect of the present invention, a data storage system isdisclosed that comprises one or more magnetic devices in a cellconfiguration and essentially each device comprising a structure oflayers including at least a first ferromagnetic layer and a secondferromagnetic layer with at least a separation layer of a non-magneticmaterial therebetween, said first structure having at least a magnetoresistance effect, and wherein the magnetization direction of the firstferromagnetic layer of at least one of said devices is irreversible inan external magnetic field higher than about 35 kA/m. The externalmagnetic field can also be higher than about 40 or 50 or 60 kA/m. Theexternal magnetic field can also be in range of about 35 kA/m to about200 MA/m.

The sensing system of the invention can be a magnetic sensor device or amagnetic read-head such as a GMR thin film head for hard disks or anysuch system including a magnetic device and signal processingelectronics for processing the signal of the magnetic characteristic ora measure or derivate thereof. The devices of the sensing system and thedata storage system of the invention can be made in a multilayerconfiguration building further on the basic GMR- or TMR-stack of thedevice. Therefore at least part of the system is manufacturable withoutsignificantly changing a standard production process to thereby make atleast part of the system at a low cost. It is possible in an embodimentof the invention to integrate the whole sensing system and/or the datastorage system of the invention on an Alsimag (a mixture of oxides)slider or on one semiconductor (silicon) chip with the multilayerconfiguration being grown or deposited on the chip. The multilayerconfiguration can be grown or deposited on the chip in the front-end orin the back-end of the process for making the chip. In the back-endprocess a part of the chip is planarized and the multilayerconfiguration is deposited or grown thereon. Appropriate connections bybonding or via structures are made in order to transfer the signals ofthe multilayer configuration to the part of the chip containing thesignal processing logic. In the front-end process, the multilayerconfiguration is directly integrated on the semiconductor (silicon). Thesensing system of the invention can also be an integrated circuit with amemory functionality and an integrated sensing system or an ASIC with anembedded non-volatile magnetic memory element and a sensing system or achipcard with a sensing system or any such sensing system. The set ofstructures of the sensing system of the invention can be made in amultilayer configuration building further on the basic GMR- or TMR-stackof the system. The layers of the devices of the systems of the inventioncan be deposited by Molecular Beam Epitaxy or MOCVD or sputterdeposition or any such technique known to the person of skill in theart.

It is also possible to apply part of, or the whole of the teaching ofthe invention, to a single magnetic device or a set of magnetic devicesthat is not in a balancing configuration. Thus the second aspect of theinvention for example can be described as a method of manufacturingmagnetic device, and the device comprising a structure of layers thatincludes at least a first ferromagnetic layer and a second ferromagneticlayer with at least a separation layer of a non-magnetic materialtherebetween, said structure having at least a magneto resistanceeffect. The method comprises the step of heating said device whileapplying an external magnetic field over said device. The heating can beachieved by applying a current pulse on or through the device.Preferably, the device or at least one of the devices of the set isheated to a temperature in the range of 50 to 800° C., preferably in therange of 100 to about 300 or 400 or 600° C. while said external magneticfield can have a value in the range of about 35 kA/m or 40 kA/m or 50kA/m to 200 MA/m.

A number of terms that is introduced hereabove and that is used in thesequel, can be described as follows, completing the understanding by theperson of skill in the art of these terms.

The term that the magnetization direction of a magnetic device isirreversible in an external magnetic field means that the magnetizationdirection may be changed under the influence of an external field, butonce the external field is switched off, the magnetization direction istaking substantially its original position from before the externalfield was applied. The magnetization direction may also remainsubstantially unchanged while exposed to the external field. Thus thepossible change of the magnetization direction is reversible. Thisirreversible characteristic is visible while evaluating the device atroom temperature and for evaluation times that are of the order of oneminute or some minutes.

A set of magnetic devices that is in a balancing configuration meansthat the configuration is such that in the response of the system thatis made out of the devices, one can clearly distinguish between theresponse or resistance changes due to (varying) magnetic field and thesensor response or resistance changes due to environmental factors suchas temperature variations. One approach in configuring such balancingconfiguration consists in connecting a number of GMR- or TMR-devices ina Wheatstone-bridge configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows how a magnetic sensing system in a Wheatstone bridgeconfiguration according to a best mode embodiment of the invention canbe achieved. FIG. 1a and FIG. 1b show how the subsequent steps oforienting the devices 1 and 4 of the Wheatstone bridge and subsequentlyoppositely orienting the devices 2 and 3 can be achieved.

FIG. 2 shows measurements on a sensing system with magnetic devices thathave opposite exchange-biasing directions and that are manufactured onthe same substrate using the method of the invention as shown in FIG. 1.The measurements show the feasibility of the invention: the reversal of2 times 2 GMR-devices in a full-bridge configuration is shown.

FIG. 3 shows schematically and in top view part of a device made inaccordance with a method of the invention.

FIG. 4 shows a Wheatstone bridge arrangement having a magnetic device inaccordance with the invention.

FIG. 5 shows a simplified view of a part of a magnetoresistive sensordevice.

FIG. 6 shows a simplified view of an arrangement comprising twoWheatstone bridge arrangements in which the magnetization direction incorresponding device are under an angle of 90°.

FIG. 7 shows a simplified view of parts of two magnetoresistive devices,stacked on top of each other.

FIG. 8 shows the layout of a sensing system according to an embodimentof the invention with a contact area in between the devices of thesystem.

FIG. 9 shows an alternate embodiment of a sensing system according theinvention with a contact area inbetween the devices of the system.

FIG. 10 shows a compact double GMR-based Wheatstone bridge for a full360 degrees angle sensing system according to another embodiment theinvention with four magnetic devices being positioned in a two by twogrouped pair-like configuration, with a first pair of devices withsubstantially the same magnetization direction of the firstferromagnetic layer of the devices under an angle of about 90 degreeswith a second pair of devices, the second pair of devices having thefirst ferromagnetic layer with substantially the same magnetizationdirection but under an angle of about 90 degrees with respect to themagnetization direction of the first ferromagnetic layer of the firstpair of devices.

FIG. 11 shows an embodiment with a 3×4 matrix configuration of compactdouble Wheatstone bridges for a full 360 degrees angle embodiment of thesensing system of the invention.

FIGS. 12a and 12 b show a deposition holder for a substrate fordepositing magnetic devices on said substrate, said holder containingmagnetic elements for applying an external magnetic field over at leastpart of said substrate, said external magnetic field having in said partat least one magnetic characteristic that is position dependent oversaid substrate. It is shown that the holder contains magnetic elementsfor applying said external magnetic field.

FIG. 13 shows a top-view and a side-view of a deposition holder for asubstrate for depositing magnetic devices on said substrate. Thedeposition holder is suited for depositing a double GMR Wheatstonebridge.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of teaching of the invention, preferred embodiments ofthe methods and of manufacturing systems of the invention are describedin the sequel. In particular, embodiments of the invention of deviceswith a magnetic multilayer configuration based on a basic GMR- orTMR-stack are disclosed. These multilayer configurations can beintegrated in the systems of the invention according to techniques knownto the person of skill in the art. It is for example possible in anembodiment of the invention to integrate the whole sensing or datastorage system of the invention on one semiconductor (silicon) chip withthe multilayer configuration being grown or deposited on the chip. Themultilayer configuration can be grown or deposited on the chip in thefront-end or in the back-end of the process for making the chip. In theback-end process a part of the chip is planarized and the multilayerconfiguration is deposited or grown thereon. Appropriate connections bybonding or via structures are made in order to transfer the signals ofthe multilayer configuration to the part of the chip containing thesignal processing logic. It will be apparent to the person skilled inthe art that other alternative and equivalent embodiments of theinvention can be conceived and reduced to practice without departingform the true spirit of the invention, the scope of the invention beinglimited only by the appended claims.

A system of the invention can be manufactured according to a method ofmanufacturing of the second aspect of the invention. In the secondaspect of the present invention, a method of manufacturing a sensingsystem of a magnetic characteristic is disclosed. The system includes aset of magnetic devices in a balancing configuration and essentiallyeach of said devices comprises a structure of layers including at leasta first ferromagnetic layer and a second ferromagnetic layer with atleast a separation layer of a non-magnetic material therebetween, saidstructure having at least a magneto resistance effect. The methodcomprises the step of heating at least one of the devices of said setwhile applying an external magnetic field over at least part of saidsystem, the part including said at least one device. Thus localizedheating of the system in an external magnetic field is achieved. Theheating can be achieved by applying a current pulse on or through thedevice. Preferably at least one of the devices is heated to atemperature in the range of 50 to 800° C., preferably in the range of100 to about 300 or 400 or 600° C. while said external magnetic fieldhas a value in the range of about 35 kA/m or 40 kA/m or 50 kA/m to 200MA/m. In the embodiment that is disclosed in the sequel, after theexecution of the steps, the first ferromagnetic layer of said at leastone device has a magnetization direction that is correlated to thedirection of said external magnetic field, and is irreversible in anexternal magnetic field higher than about 50 kA/m.

FIG. 1 shows how a magnetic sensing system in a Wheatstone bridgeconfiguration according to a best mode embodiment of the invention canbe achieved. The whole sensing system (10) comprising four magneticdevices (1-4) in a Wheatstone bridge configuration is brought in anexternal magnetic field (indicated by the vertical arrows (5)) and iselectrically connected as indicated in FIG. 1a. The curved arrows on thefigure indicate where the current pulses to achieve local heating of thedevices will flow. An external field with a magnitude of about 200 kA/mis applied. The magnetic devices consist of a multilayer configurationthat is made by sputter deposition. The multilayer configuration isdeposited on a substrate of silicon and comprises subsequently:

a buffer layer to induce the right material structure ((111) texture, inthis case) in the multilayer; in this case the buffer layer is a stackof 3.5 nm Ta/2.0 nm Ni₈₀Fe₂₀;

a first structure containing:

a layer structure consisting of an exchange-biased AAF, in this case10.0 nm Ir₁₉Mn₈₁/4.5 nm Co₉₀Fe₁₀/0.8 nm Ru/4.0 nm Co₉₀Fe₁₀; theCoFe/Ru/CoFe stack is used as the first ferromagnetic layer (the pinnedlayer);

Ir₁₉Mn₈₁ (the exchange biasing layer) has been chosen as the exchangebiasing material because of its high blocking temperature (around 560 K)for a good temperature stability the use of an AAF as pinned layerprovides an excellent magnetic stability because of its very small nettmagnetization, resulting in a great rigidity;

a separation layer of 3.0 nm Cu.

a free layer (the second ferromagnetic layer) of 0.8 nm Co₉₀Fe₁₀/3.5 nmNi₈₀Fe₂₀/0.8 nm Co₉₀Fe₁₀ (the thin Co₉₀Fe₁₀ layers enhance the GMR ratioand limit interlayer diffusion, thereby improving the thermalstability); and the multilayer configuration further comprises:

a high-resistive metallic layer of 2.5 nm Ta;

a second structure comprising

a second pinned layer consisting of 4.0 nm Co₉₀Fe₁₀ exchange-biased with10.0 nm Ir₁₉Mn₈₁;

and finally

a cap layer of 10.0 nm Ta for protection.

The current pulses to achieve local heating of the devices preferablyare such that the resulting heat dissipation heats the device above theblocking temperature. Only this part of the sensing system which isheated above the blocking temperature will permanently attain thedirection of the external magnetic field. If all bridge devices areoriginally oriented in the opposite direction (during deposition), thissingle setting step may be sufficient to realize a full-bridgeconfiguration. If desired, however, the heating procedure can berepeated. This setting procedure can be repeated with different fielddirections as often as desired. This enables, for example, in an elegantway to make two Wheatstone bridges which are mutually rotated over 90°on a single substrate; this is desired for a GMR angle sensor with a360° range.

FIG. 2 shows measurements on a sensing system with magnetic devices thathave opposite exchange-biasing directions and that are manufactured onthe same substrate using this method. The dashed lines show the voltageoutput of a GMR Wheatstone bridge prior to the application of themethod. The solid line shows the output after both pairs of GMR deviceshave been reversed by the method of this aspect of the invention. Inthis case a field of 200 kA/m and a heating current of several tens ofmA is used. This demonstration also proves that it is possible toreorient locally, i.e. reorienting one element without reorienting aneighboring element. The advantages of applying the method of thisaspect of the invention include:

Enabling the realization of GMR or TMR devices comprising multipleexchange-biasing directions with only a single deposition step;

Applicable for materials with robust exchange-biasing characteristics;

Full Wheatstone-bridge configuration are possible;

No integrated conductors for setting the magnetization directions(requiring several extra processing steps) are needed, thus a moresimple processing is achieved.

This method poses no strict limit to the smallest dimensions in thestructure of the sensing system;

Elements belonging to different bridge branches can be distributedaltematingly over the system;

This method can easily be combined with a testing step in themanufacturing process;

Provides a method to reset or repair magnetization directions insensors, read elements and MRAMs after production;

The method can be used even in finished (packaged) systems or devices.

According to a fourth aspect of the method in accordance with theinvention, in a first deposition step a first ferromagnetic layer of oneof the two opposite devices, of the sensing system is deposited, duringwhich deposition in a magnetic field is applied to pin the magnetizationdirection in the first ferromagnetic layer in a first direction, afterwhich in a second deposition step a second ferromagnetic layer of theother of the two said devices is deposited, during which deposition amagnetic field is applied to pin the magnetization direction in thesecond ferromagnetic layer in a second direction different from,preferably opposite to the magnetization direction in the firstferromagnetic layer.

In an embodiment of the invention the at least two pinned ferromagneticlayer are fabricated in at least 2 separate deposition steps, and duringthe deposition steps a magnetic field is generated by which oppositemagnetic directions are imparted to the said pinned ferromagneticlayers. Preferably this is achieved by using magnetic fields of opposingdirection during the first and second deposition step. Compared tomethods in which magnetic fields are used with the same direction but inwhich the position of the device is changed such methods are simpler.

Preferably the magnetic field that is applied during the seconddeposition has a direction different from, preferably opposite from thedirection of the field applied during the first deposition, while theposition of the device during deposition is the same. Alternatively, butless favored, the magnetic field applied during deposition is the same,but the position of the device is changed between depositions to effectthe same result. Although the method is applicable for manufacturing asensing system having for example a half-Wheatstone bridge arrangementit is of importance also for a system having four bridge devices in aWheatstone bridge arrangement.

FIG. 3 shows schematically a top view of a device made in accordancewith the method of the fourth aspect of the invention.

The embodiment shown in FIG. 3 comprises four bridges devices 31, 32, 33and 34 in a Wheatstone bridge arrangement. Each of these devicescomprises a free ferromagnetic layer and a pinned ferromagnetic layerseparated by a separation layer. The magnetic direction in each of thepinned layers of the respective elements is in FIG. 1 indicated by anarrow. Adjacent elements (within the Wheatstone bridge arrangement) haveopposite magnetic directions for pinned layers.

For example, a bridge structure as shown in FIG. 3 can be realized asfollows. First a GMR film is deposited on a substrate while a magneticfield is applied in the downward direction (at least during depositionof the pinned layer, for the free layer the field may be rotated over90° to reduce hysteris). Using lithographic techniques elements (31) and(34) are defined and fabricated out of this film. After that, a GMR filmis deposited for the second time, but now the field is applied in theupward direction. This film is patterned into the elements (32) and(33). Finally contact leads can be added in a third lithographic step.In this method it is preferred that the GMR films of both depositionshave the same magnetoresistive properties. FIG. 4 shows the equivalentdiagram of a Wheatstone bridge, having magnetoresistive sensor devices(41, 42, 43, 44) in accordance with the invention, and a current source1 for a current I_(in) connected to the terminals 46 and 47. The outputvoltage V1−V2 is present across the terminals 48 and 49. The bridge canbe operated by voltage control or current control. In comparison withvoltage control, the current control shown here offers the advantagethat a decrease of the output voltage V1−V2 in the event of anincreasing temperatures due to a decrease of the relativemagnetoresistive effect, is aptly compensated for by an increase of theabsolute value of the magnetoresistive elements 41, 42, 43 and 44 in thebridge which is caused by a positive temperature coefficient of theresistive material. FIG. 5 shows the construction of a part of amagnetoresistive sensor device as can be used according to theinvention. Arrow M_(F) in FIG. 5 denotes the direction of the anisotropyaxis of free ferromagnetic layer F and an arrow M_(P) denotes thedirection of the magnetization of pinned ferromagnetic layer P. Layers Fand P are separated by a non-ferromagnetic layer L. The element isprovided on a substrate S. An arrow 56 denotes the component of amagnetic field H to be measured which is directed parallel to themagnetization direction of the second layer P. In the magnetoresistivedevice 41, 42, 43 and 44 the easy magnetization direction of thesensitive ferromagnetic material of the layer F extends substantiallyperpendicularly to the magnetization direction of the ferromagneticlayer P. During the manufacture of the sensor devices the magnetizationdirections of the ferromagnetic layers (F and P) are laid down so thattwo elements in two adjacent (in the electrical scheme) branches of thebridge exhibit an opposed sensitivity to external magnetic fields. Thelayers may be deposited by various known method such as by sputterdeposition, MBE (Molecular Beam Epitaxy), or ion beam deposition. Duringdeposition a magnetic field is applied which determines the magneticdirection of the layer. Moreover, in each magnetoresistive sensorelement the magnetization of a ferromagnetic layer F is adjustedsubstantially perpendicularly to the magnetization direction of theother ferromagnetic layer P. As a result of these steps it is achievedthat auxiliary fields are no longer required for the measurement ofsmall magnetic fields, that the sensor is substantially free ofhysteresis and that it has an enhanced linearity.

The free layer may be a single CoFe layer, or a plurality of sublayers(e.g. CoFe+NiFe, CoFe+NiFe+CoFe, etc.) Instead of CoFe, Co or CoNiFe maybe used, but if CoNiFe is used, it should preferably not be contiguouswith the Cu spacer layer. An AAF may be used and may comprise aplurality of ferromagnetic and non-magnetic layers. Each ferromagneticpinned layer may be composed as described with respect to the freelayer. The device may comprise a combination of two pinned ferromagneticlayers and a free ferromagnetic layer. The device can also be used as adata storage cell. An angle set between the magnetization directions ofthe free and the pinned layer is representative for e.g. a “0” or a “1”.The data content can be read out by measuring the resistance of thememory cell.

FIG. 6 schematically shows an embodiment in which two Wheatstone bridges60 and 69 are made. The magnetization directions of the pinned layers61′, 62′, 63′ and 64′ in Wheatstone bridge 69 are oriented under anangle of 90° to the corresponding elements in Wheatstone bridge 60. Suchan arrangement can for instance be advantageously used to measurerotating magnetic fields. The signals V1−V2 and V1′−V2′ will enable tomeasure the magnitude as well as the angle (orientation) of the magneticfield to be measured. If the field to be measured has a magnitude sostrong that the directions of the magnetization of the free layersfollow the direction of the magnetic field to be measured, the signalsare a measure of the orientation of the magnetic field independent ofthe strength of the magnetic field. Using two Wheatstone bridges inwhich the magnetization directions in corresponding elements form anangle to each other, preferably, but not restricted, to 90° enables tomeasure the direction of the magnetic field over the full 360° range. Inall examples the directions of magnetization or of anisotropic axes areindicated as lying in the plane of the films and being substantiallyopposite to each other (at least within one Wheatstone bridgearrangement). Although such methods and arrangements are preferred andadvantageous, the invention, in its broadest sense, comprises methods inwhich the magnetization directions are different, which includes atangles different from 180°, for instance 90°. Also the directions neednot have to be in the plane of the layers, they may be or have acomponent transverse to the layers.

The following advantages of systems manufactured according to thisaspect of the invention include:

Also applicable for materials with robust exchange-biasing;

Full Wheatstone-bridge configuration are possible;

No integrated conductors for setting the magnetization directions(requiring several extra processing steps) are needed;

The method places no limit on the smallest dimensions in the sensingsystem;

Elements belonging to different bridge branches can be distributedalternatingly over the system;

Possibility to stack elements on top of each other (with isolation inbetween), thus reducing the total system area by a factor of 2 andimproving the performance of the bridge (due to smaller influences oftemperature or field gradients);

Alternatively elements can be positioned at both sides of the substrateon which the system is built.

The possibility to stack devices is schematically shown in FIG. 7. Thebridge elements 71 and 72 are stacked on top of each other, themagnetization directions MP, MP′ of the pinned layers P in elements 71and 72 are of opposite direction.

FIG. 8 shows the layout of a sensing system according to an embodimentof the invention with a contact area inbetween the devices of thesystem. FIG. 8 shows a layout of a sensing system with fourmeander-shaped GMR devices located on opposite sides of the four contactpads (86). One meander strip is forming one element of the Wheatstonebridge. The pads are lined up to provide maximum separation between thetwo pairs of devices of the Wheatstone bridge while making efficient useof the total area of the substrate (a single chip). The contact pads aretypically about 100×100 μm² with a spacing of 50 μm. The separationbetween the devices is therefor about 600 μm which is about thethickness of a Si wafer (80) which can be used as a substrate. Thisthickness is relevant since the bias magnets that can be used to createa magnetic field while depositing the device, have to be positionedbehind the substrate. Therefor, the substrate thickness sets a minimumlength scale over which the direction of a magnetic bias field can bechanged. If necessary, the Si wafer can be grinded before deposition toreduce the substrate thickness. The width of a single element meandercan be about 75 μm which is sufficient to structure 7 strips of 5 μmwith 10 μm period. Combined with a strip length of 300 μm this shouldgive a bridge resistance of over 4 kΩ which is sufficiently large. In analternate embodiment, the separation between the GMR-devices can also beused for flux guide structures or for integrated circuit with signalprocessing functionality made in the Si substrate.

FIG. 9 schematically shows 14 sensors aligned next to each other on awafer together with the required magnetic field directions duringdeposition of the devices. The lengths l₁ and l₂ define the requiredlength scale over which the magnetic field has to change direction.

The local field direction during deposition of the device is indicatedby the horizontal arrows (90).

A deposition holder according to the fourth aspect of the invention isshown in FIGS. 12a and 12 b which show a side view of a depositionholder for a substrate (120) for depositing magnetic devices on saidsubstrate. The holder contains magnetic elements for applying anexternal magnetic field that has at least one magnetic characteristicthat is position dependent over said substrate (120). The magneticelements are permanent magnets or electromagnets (127) that in FIG. 12aare alternated with soft magnetic flux guide pieces (128). In FIG. 12b,a soft magnetic backing plate (129) is provided on the depositionholder. The flux lines of the external magnetic field that is generatedby the permanent magnets or electromagnets (127) are shown by the curvedlines. The deposition holders give rise to an alternating magnetic fieldat the top side of the substrate (120). Both deposition holdersbasically give the same magnetic field pattern. The magnetic field atmaximum strength is of order of 16 kA/m or higher.

FIG. 13 shows a top-view and a side-view of a deposition holder of asubstrate (130) for depositing magnetic devices on said substrate (130).The deposition holder is suited for depositing a double GMR Wheatstonebridge. The holder contains magnetic elements for applying an externalmagnetic field that has at least one magnetic characteristic that isposition dependent over said substrate. The magnetic elements arepermanent magnets or electromagnets (137) and has a soft magneticbacking plate (139) is provided on the deposition holder. The flux linesof the external magnetic field that is generated by the permanentmagnets or electromagnets (127) is shown by the curved lines in the sideview and by the straight lines in the top view figure.

What is claimed is:
 1. A sensing system of a magnetic characteristic,said system including a set of magnetic devices in a balancingconfiguration and essentially each of said devices comprising astructure of layers including at least a first ferromagnetic layer and asecond ferromagnetic layer with at least a separation layer of anon-magnetic material therebetween, said structure having at least amagneto resistance effect, and wherein the magnetization direction ofthe first ferromagnetic layer of at least one of said devices isirreversible in an external magnetic field with a value that is higherthan about 35 kA/m.
 2. The sensing system as recited in claim 1 whereinthe magnetization direction of the first ferromagnetic layer of at leastone of said devices is irreversible at room temperature.
 3. The sensingsystem as recited in claim 1 wherein at least one of said devices isirreversible in an external magnetic field with a value in a range ofabout 40 kA/m to about 200 MA/m, preferably in a range of 40 kA/m toabout 2 MA/m.
 4. The sensing system as recited in claim 1 wherein atleast one of said devices includes an AAF-structure.
 5. The sensingsystem as recited in claim 4 wherein said first ferromagnetic layercomprises an AAF-structure, and an exchange biasing layer, preferablymade of IrMn, FeMn, NiMn, PtMn or NiO type material, said exchangebiasing layer being adjacent to, and in contact with, the AAF-structure.6. The sensing system as recited in claim 1 having at least two magneticdevices being positioned in a grouped configuration with a contact areabetween the groups and with the magnetization direction of the firstferromagnetic layer being substantially opposite for the devices of thedifferent groups and being substantially identical for the devices ofthe same group.
 7. The sensing system as recited in claim 1 having atleast two magnetic devices being positioned in a grouped configurationwith a first group of devices with substantially the same magnetizationdirection of the first ferromagnetic layer of the devices under an angleof about 90 degrees with a second group of devices, the second group ofdevices having the first ferromagnetic layer with substantially the samemagnetization direction but under an angle of about 90 degrees withrespect to the magnetization direction of the first ferromagnetic layerof the first group of devices.
 8. A data storage system comprising atleast one magnetic device in a cell configuration and said devicecomprising a structure of layers including at least a firstferromagnetic layer and a second ferromagnetic layer with at least aseparation layer of a non-magnetic material therebetween, said structurehaving at least a magneto resistance effect, and wherein themagnetization direction of the first ferromagnetic layer of at least oneof said devices is irreversible in an external magnetic field higherthan about 35 kA/m.
 9. A method of operating a magnetic system, saidsystem including a set of magnetic devices and essentially each of saiddevices comprising a structure of layers including at least a firstferromagnetic layer and a second ferromagnetic layer with at least aseparation layer of a non-magnetic material therebetween, said structurehaving at least a magneto resistance effect, the method comprising thestep of alternating at least one of the magnetic characteristics of atleast one of the devices of said set by heating part of said systemcomprising said at least one device of said set while applying anexternal magnetic field over at least part of said system, the partincluding said at least one device.
 10. A method of resetting orrepairing or changing a magnetic system, said system including a set ofmagnetic devices and essentially each of said devices comprising astructure of layers including at least a first ferromagnetic layer and asecond ferromagnetic layer with at least a separation layer of anon-magnetic material therebetween, said structure having at least amagneto resistance effect, the method comprising the step of alternatingat least one of the magnetic characteristics of at least one of thedevices of said set by heating part of the system including said atleast one device of said set while applying an external magnetic fieldover at least part of said system, the part including said at least onedevice.